The goal of this research project is to examine the mechanisms of amyloid accumulation and pathogenesis in Alzheimer's disease (AD). The specific model to be tested is that an intracellular pathway exists in cells that have been "seeded" with insoluble Abeta1-42 aggregates for amyloid production and accumulation in the solid-phase. This pathway is based on the observation that the core structure of the aggregated Abeta1- 42 peptide is resistant to degradation and accumulates within the late endosomes or lysosomes of all cells examined to date. Once nucleated, the aggregates can only grow. In APP-expressing cells, they appear to grow by the addition of misfolded, potentially amyloidogenic fragments of APP onto the Abeta1-42 lattice, followe3d by their slow conversion to more Abeta1-2 lattice, followed by their slow conversion to more Abeta1-42 by the non-specific digestion of parts of the APP molecule that are outside of the cores. The first Specific Aim will address key mechanistic questions about this pathway such as how resistant to degradation is the amyloid core and why is it resistant. We will determine whether the amyloidogenic APP fragments actually co-aggregate with Abeta1-42 and whether this interaction confers resistance to degradation to the Abeta1 core of these APP fragments. We have also observed that some of the Abeta1-42 molecules that are internalized and accumulate appear to be post-translationally modified by oxidation. Specific antibodies against oxidatively modified Abeta will be used to examine whether the amyloid that accumulates in extracellular amyloid plaques is derived from this Abeta that is post-translationally modified within the cell. We will determine the cells responsible for the modification and the subcellular localization of the site of this modification. We also propose to examine whether this oxidative modification is related to the resistance to degradation and accumulation of the peptide. Recent evidence from investigation of vaccinating transgenic mouse models of amyloid accumulation against Abeta suggest that vaccination may facilitate the degradation and clearance of amyloid. We will test the effectiveness of a variety of abeta1-interacting macromolecules for enhancing the degradation of Abeta1-42 or its intracellular accumulation.